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LONDON, England -- British police said they believed it was "very likely" that at least one of the bombers responsible for last week's terrorist attacks in London died in the explosion near Aldgate station.

Deputy Assistant Commissioner Peter Clarke, head of the Metropolitan Police's Anti-Terrorist Branch, told a news conference officers were trying to establish whether four men suspected of carrying out the bombings had all been killed.

One man has been arrested and six arrest warrants issued following a series of raids around Leeds in West Yorkshire, 310 kilometers (190 miles) north of London, in connection with the investigation, Clarke said.

Police had forensic evidence linking four men -- three from West Yorkshire -- to the scenes of all four of last Thursday's bomb blasts on the underground and bus networks, he added.

One of the men from West Yorkshire had been reported missing by his family. Property belonging to him had been found at the site of the Tavistock Square bus blast.

Clarke said all four had arrived in London by train at King's Cross station on the morning of the attacks. All three of the bombed underground trains passed through the station.

British army bomb disposal experts earlier carried out a controlled explosion to gain access to a house in the Hyde Park area of Leeds.

Hundreds of residents from surrounding streets had to be evacuated as armed police stood guard outside the house.

Police also raided five other houses in the Leeds area and carried out a controlled explosion on a car parked at Luton railway station.

West Yorkshire Police said that Metropolitan Police detectives backed by local officers had mounted a "pre-planned, intelligence-led operation."

Clark confirmed that material had been seized and that measures had been taken to prevent any danger to the public.

In Luton, 50 kilometers (30 miles) north of London, Bedfordshire police said they had sealed off the area around a vehicle suspected of being involved in the attacks.

"Police believe the vehicle may be connected to the terrorist attacks in London on July 7 and it will be examined in the car park for safety reasons before being taken away to a secure location," police said in a statement.

Tuesday's raids were the first reported operation in a crime investigation described by British Prime Minister Tony Blair as "among the most vigorous and intense that this country has ever seen."

"We will pursue those responsible -- not just the perpetrators, but the planners of this outrage, wherever they are. And we will not rest until they are identified and, as far as humanly possible, brought to justice," Blair told the House of Commons on Monday.

Blair and other relevant ministers were being kept informed of Tuesday's operation, the Prime Minister's official spokesman told PA.